Since the middle 1970's catalytic converters have been required equipment for treatment of the exhaust from internal combustion engines in vehicles. The primary purpose of these devices is to convert by catalytic means noxious exhaust components of hydrocarbon fueled engines into harmless materials, e.g. carbon dioxide, water and nitrogen, and more recently to trap and oxidize products of incomplete combustion, e.g. particulates such as carbon frequently generated in annoying quantities by diesel powered engines.
Up to the present time, the supports for the catalyst or catalysts and particulate traps which effect the desired pollution reducing effects have been made from ceramic materials in the form of the familiar "honeycomb". The inner walls of these monolithic honeycombs are coated with a precious metal catalyst, or a plurality of catalysts, such as platinum, palladium and/or rhodium.
Hot exhaust gas coming into contact with the surfaces carrying the catalyst material undergoes chemical change to harmless materials. An early embodiment of a metallic catalyst carrier is described in U.S. Pat. No. 1,636,685 dated July 26, 1927 and issued to Downs. According to Downs, iron particles are treated by dipping into melted aluminum or by milling with powdered aluminum.
In a process called calorizing there takes place an alloying action between the aluminum and iron. The iron/aluminum surface provides a very satisfactory surface upon which to deposit catalytic materials, e.g., oxide catalysts such as metal of Groups V and VI of the Periodic Table. These structures are adapted for vapor phase catalytic oxidation of organic compounds.
U.S. Pat. No. 2,658,742 dated Nov. 10, 1953 to Suter et al discloses a metallic catalyst support for removing harmful ingredients from exhaust streams. Platinum and palladium are disclosed as useful to aid in combustion of combustible materials, e.g. carbon monoxide. Stainless steel is disclosed as a base metal for the catalyst. The base metal may be in the form of a wire or screen or other physical form. Another patent to Suter, U.S. Pat. No. 2,720,494 dated Oct. 11, 1955 discloses a process for the preparation of a catalytic element. Platinum or palladium or a mixture of the two noble metals in a catalytically active form may be used on a metallic substrate such as stainless steel, Nichrome or Chromel.
Bernstein et al in U.S. Pat. No. 3,773,894 disclose a metallic catalyst supported on a metallic substrate as a catalytic converter for internal combustion engine exhaust gas. Various physical forms of the catalyst support are shown including a spiral wound screen and a cordierite honeycomb.
U.S. Pat. No. 3,059,326 dated Oct. 23, 1962 discloses iron/aluminum cores having substantial oxidation resistance.
U.S. Pat. No. 3,254,966 to Bloch et al dated June 7, 1966 discloses a structure for effecting catalytic conversion of exhaust gas streams. The catalytic element includes a housing having spaced perforate walls, a mat of strand-like, all metal catalytic material filling the interior of the housing, a plurality of relatively small perforate containers in spaced relationship within the compact mat and surrounded by the all-metal catalytic material, and a filling of particulate catalyst, e.g. alumina spheres coated with a catalytic material of the platinum metal group.
Other U.S. Patents of interest in this field include the patent to Brewer U.S. Pat. No. 3,867,313 dated Feb. 18, 1975 relating to an all-metal catalyst element provided by depositing a noble metal, e.g., platinum and/or palladium plated or deposited onto a nickel-free aluminum, chromium and iron alloy. The patent to Oshima U.S. Pat. No. 3,873,472 also related to a catalytic system for treating exhaust gases. The base metal is an iron/aluminum alloy. Before application of the catalyst, any aluminum oxide on the surface of the substrate is carefully removed. See also U.S. Pat. No. 3,903,020 dated Sept. 2, 1975 to Sergeys et al which discloses the use of ceria as a stabilizer and activator for the catalyst. See also U.S. Pat. No. 3,907,708 to Lacroix dated Sept. 23, 1975 directed to a metal support, a metal aluminide layer, and a catalytic surface layer on an alumina layer of the gamma or eta type. Various catalyst element structures are shown. U.S. Pat. No. 3,957,692 to Cairns et al dated May 18, 1976 discloses another method of preparing a catalyst by sputtering and bombarding with a source of energetic ions.
Volker et al U.S. Pat. No. 4,188,309 dated Feb. 12, 1980 discloses various shaped catalysts utilizing a structural reinforcing agent consisting of iron or steel, an iron aluminum diffusion layer and a catalyst. U.S. Pat. No. 4,300,956 dated Nov. 17, 1981 to Rosenberger et al discloses a convolute-wound corrugated/non-corrugated metal sheet having metal-to-metal diffusion bonds. The unbonded surfaces are oxidized to improve their adhesion to the later applied catalyst.
The Retallick U.S. Pat. No. 4,301,039 dated Nov. 17, 1981 discloses a method of making a metal catalyst support in a spirally wound form whereby indentations in the surface will not nest together. U.S. Pat. No. 4,318,888 dated Mar. 9, 1982 and issued to Chapman et al discloses a spirally wound foil structure having a corrugated surface and distinct catalysts on confronting surfaces.
U.S. Pat. No. 4,402,871 to Retallick and issued on Sept. 6, 1983 discloses a honeycomb catalyst support formed by folding a single layer of metal back and forth upon itself. Each layer in the honeycomb has indentations of uniform height so that the spacing between layers is equal to this height. A different pattern of indentations is used on alternate layers, and the indentations are on opposite sides of the strip in alternate layers. This structure prevents nesting of confronting layers.
The more recent structures are made of a thin ferritic stainless steel strip of the type referred to by Kilbane in patent application Ser. No. 741,282 filed June 4, 1985, and by Retallick in patent application Ser. No. 738,485 filed May 28, 1985, corrugated and fan folded or folded back and forth upon itself. The surface of the strip is provided with a catalytically active agent for decontaminating an exhaust gas, e.g., the exhaust gas generated by an internal combustion engine. Reference may also be had to Cornelison patent application Ser. No. 796,710, filed Nov. 12, 1985, which discloses a catalytic fan-folded element of the type which can be produced by the present process.
Honeycombs made according to a preferred practice of the present invention cannot telescope. These honeycombs are made by folding a single strip of metal back and forth upon itself. The folded strip is placed in a canister and then the folded strip is anchored in the canister by a lip, a flange, or a crimp that goes around the periphery of the core formed from the folded strip. Every layer of the core is anchored individually so that there can be no telescoping.
Another method of anchoring each layer individually is shown in U.S. patent application Ser. No. 650,085, entitled "Catalytic Converter for an Automobile".
A principal object of this invention is to provide a process for making a catalytically active core for a catalytic converter, and in more specific aspects a continuous process for making such cores and ultimately placing the cores so made in a suitable housing. This process has a number of advantages over the commonly used ceramic cores: (1) the entire operation can be carried out at a single location instead of two or more locations, (2) labor and transportation are greatly reduced, (3) very wide cores (over 6" length) can be coated front to back and along the length of the strip uniformly, (4) cores can be selectively coated front to back and (5) the face cross section of the catalyst can be of any geometric configuration.